Vertical coupling impedance of the APS storage ring

The three-dimensional wake potentials of the APS storage ring have been reconstructed according to the impedance database concept. Every wakefield-generating component in the ring was considered including small-gap insertion device (ID) chambers, rf cavities, shielded bellows, beam position monitors, synchrotron radiation absorbers, scrapers, flags, various chamber transitions, septum chambers, and pulsed kickers. In this paper the result for the vertical wake potentials and its impedance are presented. Dominant contributors are the ID chambers whose heights are 5 mm and 8 mm. Since more small-gap chambers are envisioned for installation in the APS storage ring, prediction of their effect on the beam is very important not only for the APS but also for all third-generation light sources. We used the vertical impedance reported here to investigate the measured tune slope and single-bunch current limit in the APS storage ring. The program elegant was used for particle tracking, and its results are presented. We also report that we observed a vertical focusing in the calculated wake potential of the shallow transition without rotational symmetry.